1. Field of the Invention
This invention relates to spatial light modulator imaging systems, more particularly to those systems requiring alignment of at least one spatial light modulator in an optical path.
2. Background of the Invention
Spatial light modulators come in many forms, including those that can be used to create images. One type of these image-forming modulators are spatial light modulator arrays, typically consisting of an array of individually controllable elements, their corresponding control circuitry, and drive electronics for accessing the control circuitry. Common example of these types of modulators are liquid crystal devices (LCDs), Actuated Mirror Arrays (AMA.TM.) manufactured by Daewoo, and Digital Micromirror Devices (DMD.TM.) manufactured by Texas Instruments.
These devices reflect or transmit incident light in a grid of dots, called picture elements or pixels. The amount of time an element is in a given state, either ON or OFF, determines the intensity of each pixel. The pixels form the image being created by the device. With just white light and non-colored elements on the device, the image appears as black and white. This would be used in monochrome display systems, or even in printing systems, where the color is formed by the use of colored toners, not the white.
Color display images can be formed in several ways. One method is to actually color the pixels themselves so that the incident light being reflected or transmitted becomes that color. Another is to use one device and either color filters, or colored light sources, where the color being imaged onto the projection surface is achieved by changing the color of the light. Yet another method is to use three devices, one for each of the additive primary colors, red, green, and blue. The latter two methods rely upon the integration of the human eye to take three "layered" images, one for each color and convert it to an image of one color.
Additionally, using either the one chip and color filter system, or the three chip system, the alignment of the device or devices in the appropriate optical path to register and focus the pixels on the display surface is critical. For example, in a three device system each device receives and reflects or transmits one color. The pixels projected from each device must exactly line up with the corresponding pixels from the other device, or the pixels will have colored edges and the picture will be blurry and oddly colored. In the one device example, the device must be situated in the proper position for the image formed by the modulator to be in focus.
Both of these problems must be solved in a manner that is easy to perform and permanent. Once the images are aligned, or registered, the devices must be locked into position. Therefore, a method and apparatus is needed that allows the alignment of spatial light modulators and holds the aligned position.